Utilizing Via-in-Pad for PCB Design and Production Techniques
Via-in-pad technology, a cutting-edge approach in the realm of Printed Circuit Board (PCB) design, involves placing plated through vias directly within the component pads instead of beside them. This technique offers several benefits, but it also presents some challenges.
Advantages of Via-in-Pad Technology
One of the primary advantages of via-in-pad technology is improved electrical performance. By shortening the signal path, it reduces inductance and enhances high-frequency performance, which is particularly beneficial in high-speed and high-density designs.
Additionally, via-in-pad allows for more compact PCB layouts by enabling higher component density, as vias do not take up additional board area outside the pads. This space-saving feature is crucial in today's miniaturised electronic components.
Via-in-pad technology also facilitates efficient heat dissipation from components to internal or back-side copper planes, improving thermal performance, especially for power devices.
Moreover, with proper via filling and plating, it can improve solder joint reliability by providing better flatness and solderability on the pad surface, enhancing assembly quality.
Disadvantages of Via-in-Pad Technology
Despite its advantages, via-in-pad technology introduces some complexities and potential issues. These include additional processing steps such as via filling (with conductive or non-conductive epoxy) and plating over to prevent solder from flowing into the vias during assembly, which raises manufacturing costs.
Improper via filling or plating may lead to solder voids or weak solder joints, posing reliability concerns, especially under thermal cycling or mechanical stress.
Moreover, since vias are under the component pads, rework can be more challenging compared to traditional via placement. There's also a risk of solder wicking without adequate via filling, causing insufficient solder on the pad leading to weak connections.
Implementing Via-in-Pad Technology
To minimise problems in manufacturing and excess cost and time for via-in-pad routing, it's recommended to stick to component manufacturer recommendations for component placement and via capping and filling, limit microvias to one layer of the PCB, ensure the non-component side is capped with a solder mask, and avoid leaving vias open unless necessary.
When using standard mechanical drilling, laser microvias may be necessary if the remaining annular ring is insufficient after specifying the smallest drill diameter. Non-conductive epoxies are often chosen for via fill due to their CTE being closer to that of laminates and cost-effectiveness.
When vias are not placed on pads, they don't need to be filled and don't need to be marked as via-in-pad in the Sierra Circuits online quoting tool. It's worth noting that the PCB's design and intent will ultimately decide the type of epoxy required for a via fill.
The manufacturing options for VIP include mechanically drilled, plated, and non-conductive-filled methods, laser-ablated and fully copper-filled via-in-pad methods. The conventional method for preventing solder from being drawn into via cavity involves using a solder mask as a plugging medium.
In summary, via-in-pad technology improves signal integrity, space savings, and thermal management but introduces manufacturing challenges, extra cost, and potential reliability concerns if not carefully implemented. It is often used in high-density, high-speed, or thermally demanding PCB designs where these advantages outweigh the added complexity. The technique requires careful control of via filling and plating processes to ensure successful assembly and operation.
For a comprehensive guide on via-in-pad technology and PCB design, the IPC Class 3 Design Guide, containing 8 chapters, 23 pages, offers guidelines for manufacturing defects, assembly processes, and common differences between the classes.
- Implementing controlled impedance technology is crucial when utilizing via-in-pad technology, as it helps maintain consistent electrical characteristics across the Printed Circuit Board (PCB).
- The benefits of via-in-pad technology extend to the field of controlled impedance technology, as it enables more precise control over impedance due to its shorter signal path and improved high-frequency performance.
